a) Field of the Invention
The invention is directed to a coordinate measurement device with an optical sensing system for non-contact sensing of edges and surface structures of measurement objects. The field of application is optical coordinate measurement technology, especially the measurements of measurement objects by means of single- or multiple-coordinate measurement devices.
b) Description of the Related Art
In an optical probe in coordinate measurement devices described in U.S. Pat. No. 5,319,442 for determining the position of surface structures in test pieces and measurement objects in relation to the moving part of the coordinate measurement device, a sensor array is provided and the structures of the measurement object are imaged thereon by means of imaging optics comprising a plurality of components. By means of sequential scanning of the individual sensors of the array, the image of the measurement object is analyzed on the sensor arrangement. As soon as the structure has reached a predetermined sensor of the sensor arrangement, a trigger signal is generated and sent to a control system of the coordinate measurement device for determining the position of the movable arm relative to the structure. A disadvantage in this device consists in the high technical complexity in evaluating the signals for obtaining measurements
DE 40 18 333 A1 describes a process and a device for the automatic detection of edges of hardness measurement indentations, wherein the hardness measurement indentation is detected by a TV camera and the obtained video signal is supplied to a comparator which has an adjustable level. The output signal of the comparator is differentiated and the contour signals thus obtained are loaded into memory. The geometric data of the measurement indentations are computed from these contour signals.
It can be seen from Publication No. 8942.5m, Part. No. H1000-315201-A by Renishaw, "VP 2 Video Scanning System", 1994, and the accompanying data sheet for a VP 2 Video scanner for coordinate measurement devices that these scanners have imaging optics with fixed focal length in which different magnifications can be achieved in that the focal plane of the objective is located at a variable distance from the objective depending on the desired magnification. The focusing required in this case is carried out by means of an axial movement (usually in the Z-axis) of the coordinate measurement device.
In order to mark or scan positions on the image of the measurement object imaged on the screen, a cross-hair or cross-line is faded in on the screen and can be moved into a wide variety of positions on the screen in two coordinates X and Y via rotary switches and tuning elements (publication of HIMMELREICH-elektronik GmbH & Co. KG, Schwaigern, Germany, "Fade-in Video Cross-hairs" data sheet).
This cross-line which is composed of two lines is generated by a reticle generator or cross-line generator, as it is called, wherein a crystal-controlled time base is provided and there is accordingly no exact relationship to the pixels.